Wheels for centrifugal fans of the forward curved multiblade type



NORIYOSHI FUJll ,1 WHEELS FOR CENTRIFUGAL FANS OF THE FORWARD CURVED MULTIBLADE TYPE 5 Sheets-Sheet 1 July 7, 1964 Filed Aug. 15. 1961 Nomyoall INVENTOR.

July 7, 1964 NORIYOSHI FUJll 3,140,042

' WHEELS FOR CENTRIFUGAL FANS OF THE FORWARD CURVED MULTIBLADE TYPE Filed Aug. 15,1961 '5 Sheets-Sheet 2 N /mull E J Q INVENTOR. [5 3 BY Mr 7v/%\ July 7, 1964 NORIYO l FU Jll WHEELS FOR CENTRIFUG FANS OF THEFORWARD CURVED MULTIBLADE TYPE Filed Aug. 15 1961 5 Sheets-Sheet s y 7, 1964 NORIYOSHI FUJll 3,140,042

WHEELS FOR CENTRIFUGAL FANS OF THE FORWARD CURVED MULTIBLADE TYPE Filed Aug. 15, 1961 5 Sheets-Sheet 4 INVENTOR.

BY Qm/ July 7, 1964 NORIYOSHI FUJI] 3,140,042 WHEELS FOR CENTRIFUGAL FANS OF THE FORWARD CURVED MULTIBLADE TYPE Filed Aug. 15. 1961 5 Sheets-Sheet 5 WW pwnoy fawnfls Q INVENTOR. fimr/rox/n FvJr/ k5 ab (uwa mm wi w Q comparatively large curvature.

United States Patent F 3,140,042 WHEELS FOR CENTRIFUGAL FANS OF THE FORWARD CURVED MULTIBLADE TYPE Noriyoshi Fuj ii, 124 Matsuzono-cho, Nishinomiya, Japan Filed Aug. 15, 1961, Ser. No. 131,600 1 Claim. (Cl. 230-134) This invention relates to centrifugal fans of the forward curved multiblade type, and, more particularly, to wheels for centrifugal fans of the forward curved multiblade type of small size for heating, cooling or ventilation. With this type of fan it is most essential that the noise should be as low as possible, and the object of the present invention is to provide means of at once lessening the noise and increasing the efficiency of fans of this type.

In the past, each blade of a centrifugal fan of the forward curved multiblade type has been made of a metal plate which is bent in a shallow gutter shape approximately conforming to air flow in and out. But, according to this type of blade, its concave front and convex back are of identical curvature, that is, it forms concentric circular arcs in section, and the curvature itself being hydrodynamically imperfect, a passage between adjacent blades does not conform to the air current therethrough. Furthermore, at the middle of the passage is formed an enlarged part, generating break away .of air flow on the blade surface together with its turbulence and branching phenomenon. Furthermore, collision of air on the inlet of the passage causes lowering of efficiency and on account of thin blades which cause inflowing loss suddenly to change when the air inlet angle varies the number of revolutions of the fan is confined within very narrow limits. Besides, air slips on the blade cause great slipping loss, and what is more, small blades are hard to manufacture.

The present invention provides a wheel for a centrifugal fan of the forward curved multiblade type of which each blade has its front formed in a shallow gutter shape conforming to air flow in and out of a passage between each two adjacent blades, with the inner edge thereof having a Its back forms such a bulging shape as makes the passage narrower by degrees from the inner end out to the outer end thereof without giving any enlarged part therebetween, and is made .of aluminium extruded by an extruding machine.

According to the present invention, not only are the above-mentioned defects of known blades of metal plate all eliminated but blades strict and uniform in form are easily provided in mass-production.

Other and further objects of the present invention will become apparent from the following specification and claim taken together with the accompanying drawings in which is shown the preferred embodiment of the runner of a centrifugal fan of the forward curved multiblade type according to the present invention.

FIG. 1 is a sectional view of a wheel for a centrifugal fan of the forward curved multiblade type embodying the present invention;

FIG. 2 is a sectional view of a wheel of this type heretofore in use;

FIG. 3 is a side view of a centrifugal fan of the forward curved multiblade type provided'with a wheel embodying the present invention;

FIG. 4 is a sectional view of the wheel;

FIG. 5 is a sectional view of a part of FIG. 4 on the line 55;

FIGS. 6 and 7 are diagrammatic views of an air passage in the wheel according to the present invention in comparison with that in a wheel of a known type;

FIGS. 8 and 9 are sectional views of the air current in the former compared with that in the latter; and

erence line.

3,140,042 Patented July 7, 1964 f we FIGS. 10 and 11 are comparative diagrams showing the result of a performance test on the two.

In these drawings reference numeral 11 indicates a blade made by extruding a long beam of aluminium of the sectional shape shown in FIG. 1 by an extruding machine and then cutting it in certain prescribed length, each of the cut ends being provided with a projection 11 for setting thereof, and the details of its sectional shape are as follows (the units are in millimeters):

B=15.5 121 5, R =8.5, R3 6, R4 12, 0.8, R5 O.4 11 6, 1 8,

The sectional shape of the front 14 of the blade 11 consists of two arcs 15 and 16 of radii R and R approximately forming an arc. The inner edge 12 and the outer edge 13 form arcs of radii R and R and the back 17 consists of an arc 19 of radius R; for the most part of it and for the rest of an are 18 of radius R which connects the are 19 and the are 12 of the inner edge. In this, R being greater than R the blade gains thickness by degrees from the outer edge inwards. B is the chord length of the blade between the leading andtrailing edges thereof and measured along a horizontal line which intersects the lower curved portions of the forward and rearward end portions of the blade. 1 is a distance which a vertical line is spaced from a first vertical line or the reference line which passes through the very inner edge of the blade, and radii R and R are located along this vertical line which is spaced a distance from the ref- In face, radius R is located at the point where this line intersects the horizontal chord B which passes through the lower edges of the blades. 1 is a distance which another vertical line is spaced from the reference line, and radius R has its center on this line. 1 is a distance which a further vertical line is spaced fromthe reference line and radius R; has its center on this line. A wheel according to the present invention is constructed by calking the projections 11 into holes on a side plate 20 and a circular side plate 21, and numeral 22 indicates a driving shaft and 23 a casing.

The front .of each blade being shaped in a shallow gutter shape conforming to air flow in and out of the passage, no slipping loss is caused between air flow and the surface of blade, and so the velocity of the air creasing by degrees from the inner end thereof outwards as shown in FIGS. 6 and 7, the air current gradually increases in velocity, so that the air flows with very high velocity out of the outer end of the passage, giving a nozzle effect.

Thus much less turbulence, branching flow, or breakaway phenomenon is generated in the passage, the noise is kept low and the blowing efficiency increases greatly.

The inner edge of the blade being given comparatively large curvature, changes the air inlet angle which varies in accordance with changes in the number of revolutions of the wheel cause so little inlet collision and loss thereby that a fan can be driven with the number of revolutions of the wheel thereof varied within a wide range. The blades are made of aluminium extruded by an extruder, which enables the mass-production of light and uniform blades strict in form. Besides, these blades, having far greater section modulus than a known type made of metal plate, get enough strength, though made of aluminium, making much less vibrating noise.

FIG. 6 shows an air passage between adjacent blades 11 according to the present invention compared with that between known blades 11 made by bending a. metal plate in a shallow gutter shape. Circles in full lines contact with the front of a blade 11 and the back of the next blade 11,,, and circles in chain lines contact with the front of a blade 11 and the back of the next blade 11 In FIG. 7 is shown a diagram in which a curve a of full line denotes radii of circles in full lines in FIG. 6, and a curve b of a chain line radii of circles in chain lines in the same, abscissas thereof denoting respectively lengths of straight lines into which the two curves connecting centers of the two groups of circles are converted. This diagram shows that the sectional shape of a passage between blades according to the present invention gradually and evenly narrows in width while that of a passage between known blades is enlarged about at the middle part of it. The curve a denotes curve a moved up- Ward in parallel and the area between the curves a and b corresponds to the difference of thickness between the blades 11 and 11 FIGS. 8 and 9 show the air current between blades according to the present invention in comparison with that between known type blades made by bending a metal plate into a shallow gutter shape. Blades according to the present invention 11,, are drawn in full lines and blades of a known type 11;, are in chain lines. In FIG. 8 blades 11 are placed just inside the fronts of the blades 11,, and on the back of the blade 11 is generated turbulence of air flow, and in FIG. 9 wherein blades 11 are placed in the middle of blades 11,, turbulence of air flow is generated on both the front and the back of each blade 11 These turbulences are lost to blades 11,, with the thickened parts thereof filling the spaces to generate turbulences.

FIGS. 10 and 11 show the result of a comparative performance test of a centrifugal fan of the forward curved multiblade type furnished with blades 11,, according to the present invention and a fan provided with known blades 11 Curve a shows performance of a fan having a connected pair of wheels 160 mm. in diameter, each provided with 36 blades 75 mm. in length, of which the sectional shape is just as illustrated above, and curve b shows performance of a fan provided with a pair of wheels connected together, each 160 mm. in diameter and having 32 blades which are made of a metal plate 0.8 mm. in thickness, 78 mm. in length and bent in a gutter shape of 10.5 mm. inside diameter. Thus it can be said that the two fans have approximately the same condition. From what the result of the performance test shows it is apparent that a blade according to the present invention is much superior to a known type in quietness and blowing efiiciency.

It is apparent that the invention and its advantages will be understood from the foregoing description and it is apparent that various changes may be made in the forms, construction and arrangement of the parts without departing from the spirit and scope of the invention, the form hereinbefore described and illustrated in the drawing being merely a preferred embodiment thereof.

Having thus described my invention, what I claim and desire to secure by letters Patent of the United States 1s:

In a centrifugal fan of the forwardly curved multiblade type, the improvement wherein each blade has its front in the shape of a shallow gutter and conforms to air flow through the passage formed between adjacent fan blades, the inner edge having a relatively large curvature, and the back having a bulging curve shape gradually diminishing the width of the passage from the inner end out, each blade having continuously curving inner and outer surfaces, each blade having a cross-sectional configuration with substantially the following proportions:

wherein B is the blade chord between the inner edge and the outer edge, is the distance of a first line from a reference line passing through the beginning of the blade chord at the inner edge, 1 is the distance of a second line from said reference line, is the distance of a third line from said reference line, all of said lines being parallel to each other and perpendicular to the blade chord, R is the radius of a portion of the inner blade surface near the inner edge and having its center on said first line, R is the radius of a portion of the inner blade surface near the outer edge and having its center on said second line, R is the radius of a portion of the outer blade surface near the inner edge and having its center on said first line, R is the radius of a portion of the outer blade surface near the outer edge and having its center on said third line, R is the radius of curvature of said inner edge, and R is the radius of curvature of said outer edge.

References Cited in the file of this patent UNITED STATES PATENTS 1,749,528 Frendenreich Mar. 4, 1930 1,910,943 Wiberg et al May 23, 1933 2,254,629 Stine Sept. 2, 1941 2,366,251 Fullemann Jan. 2, 1945 2,439,933 Jenkins Apr. 20, 1948 2,856,675 Hansen Oct. 21, 1958 2,991,004 Denbo et al. July 4, 1961 FOREIGN PATENTS 153,419 Austria May 25, 1938 3,253 Great Britain of 1878 710,391 Great Britain June 9, 1954 495,846 Italy Jan. 25, 1954 

